The present invention relates generally to a method of and apparatus for controlling the supply of fluid. More particularly, this invention relates to a method of and apparatus for controlling the edge of processing fluid distributed between a pair of converging sheets, just prior to the sheets becoming superposed to each other.
A variety of photographic processes of the self-developing type broadly involve the application of a viscous liquid reagent across exposed photographic sheet material. Typically, in these processes, a photosensitive sheet is first exposed and then later superposed with respect to a second sheet. The two superposed sheets are then moved between a pair of juxtaposed pressure applying members. The pressure applying members are constructed and arranged so as to spread the fluid from this mass, in an approximately uniform layer, over a desired exposed portion of one of the sheets. The spread processing fluid can initiate formation of visible images.
Significant problems can arise in connection with distributing the fluid in such a manner. One is to maintain a sufficient amount of fluid over the exposed areas of a sheet. This is for the obvious reason that it is critical for complete image formation that the amount of processing fluid be accurately and uniformly spread out over such exposed area. Secondly, it is also important to contain the processing fluid within the desired confines of the side marginal edges of the sheets. Otherwise, of course, processing fluid falling beyond such edges would contaminate the pressure applying rollers and other equipment associated with the processing of the photosensitive sheets. Variations in the amount of processing fluid distributed at any given time can arise in situations wherein the viscosity of the fluid changes. Thus, when attempting to dispense controlled amounts of such fluid, these variations can increase or decrease the amount dispensed. Thus, significant problems can arise in trying to keep the lateral edge of the fluid from spilling off the lateral edges of the sheet while insuring that the fluid covers the exposed area for complete developing. Such considerations are particularly crucial when it is desired to process large quantities of film and there is a relatively narrow space between the lateral margins and exposed areas of the sheets.
There have been a number of approaches for controlling the distribution of such processing fluid. One makes provision for having side rails on a film sheet which are capable of confining excess liquid within the side marginal edges. Another solution, disclosed in U.S. Pat. No. 3,120,794, describes one of the processing rollers having a pair of axially spaced apart sealing elements for purposes of confining the dispensed fluid within the side margins of the sheets. U.S. Pat. No. 3,307,467 discloses spring-biased pressure applying members which prevent escape of the liquid from between the lateral margins of the sheets as the sheets are advanced through a gap between the pressure applying members. U.S. Pat. No. 4,162,834 discloses a pair of laterally spaced nozzle members which direct streams of air at opposite ends of a longitudinal processing fluid puddle. U.S. Pat. No. 2,563,343 discloses an approach for controlling the supply of processing fluid within the marginal edges. In this approach, a liquid gauging system is provided which, in one mode, includes a pair of spaced electrical contacts. Each one is positioned adjacent a lateral marginal edge of a liquid holding space. The contacts are pressed against the edges of one of the two sheets being superposed. Normally, the contacts do not touch the processing fluid. However, when an excess amount of liquid exists within the holding space, it tends to contact both switches. As this happens, an electrical connection is created between the two contacts for causing operation of a solenoid so as to open a switch. The switch is then responsible for operating a valve which restricts the fluid dispensed. U.S. Pat. No. 2,719,789 discloses a similar process by which liquid is prevented from going beyond the lateral marginal edges of the processing sheets. Disclosed is the fact that one of the film sheets is provided with a succession of conducting strips along each lateral marginal edge. The strips cooperate with spaced apart brushes so as to form part of an electrical control circuit. When fluid covers both conducting strips, the circuit is operative to control a solenoid which, in turn, controls a valve for restricting fluid flow.
None of the foregoing approaches, however, disclose a system which can simply and conveniently control distribution of processing fluid to an area adjacent a marginal edge of a photographic sheet, let alone one which can reliably control the edges of fluid distributed within a preselected zone of the sheet wherein one edge of the zone is adjacent a marginal edge of the sheet and an opposite edge of the zone is adjacent a preselected portion of the sheet.